Hitherto, there have been known projection-type image display apparatus including a light source, an optical modulator configured to modulate light emitted from the light source, and a projection unit configured to project, on a projection surface, the light being modulated by the optical modulator.
In many cases, the related-art projection-type image display apparatus employ a lamp as a light source configured to generate light of three primary colors, and are configured to separate white light, which is emitted from the lamp, with a dichroic mirror into three primary colors: red (R), green (G), and blue (B), modulate the three primary colors based on image information, synthesize the modulated colors with a synthesizing prism, and display the resultant on a screen through a projection lens.
In recent years, demands for a still higher luminance (higher output), a wider color gamut, and a longer life have been increased. However, it is difficult to achieve a still higher luminance with a lamp light source because the lamp light source causes problems such as increase in heat generation amount, increase in cooling structure in size, noise, and increase in power source in size. It is also difficult to achieve a wider color gamut and a longer life with a lamp light source.
In view of the above, in recent years, there have been developed, instead of a lamp light source, light sources using a plurality of semiconductor lasers or LEDs having a wide color gamut and long life as light source elements, thereby being capable of obtaining high output, and projection-type image display apparatus using such light sources.
In order to cause semiconductor lasers, LEDs, and other elements of respective colors (R, G, and B) to stably emit light or oscillate, it is important to keep operating setting temperatures thereof constant. When a light source element is a semiconductor laser, the light emission efficiency of the semiconductor laser increases as the temperature of the semiconductor laser decreases. In general, Peltier elements are used in a technology for cooling semiconductor lasers. However, heat loads of those elements are large, and hence there arise problems such as increase in heat pipe and heat sink in size, increase in noise due to increased air volume of fans, and increase in power consumption.
Meanwhile, a cooling method using water cooling can suppress heat loads as compared to a case of using Peltier elements. However, there is a significant difference between the temperatures of water at an inlet of a cooler and at an outlet thereof, and hence temperatures of a plurality of semiconductor lasers cannot be kept constant. As a result, stable output light cannot be supplied.
As one method for solving the problems described above, there has been proposed a method in which a cooling apparatus including a refrigerant circuit including a compressor, a condenser, a fan, a pressure reducer, and an evaporator (cooler) is used, and latent heat generated by vaporization of refrigerant is utilized (for example, see Patent Literatures 1 and 2).
In Patent Literature 1, there is proposed a system in which temperature is kept constant by connection of refrigerant pipes to light source elements directly or indirectly through heat pipes. Meanwhile, in Patent Literature 2, there is proposed a system in which temperature is adjusted by controlling heating units provided to light source elements.